1. Field of the Invention
The present invention relates to a method for increasing the elasticity, flexibility, ductility, and resiliency of fibers, and strings for musical instruments, fishing equipment, and sports racquets.
2. Description of the Prior Art
For fibers and strings used on stringed musical instruments, fishing equipment, and stringed sports racquets, it is advantageous that the fibers and strings have a high degree of elasticity (low modulus of elasticity or low dynamic modulus of elasticity), flexibility, ductility, and toughness while having high breaking strength, resiliency (low internal damping), and abrasion resistance. In the case of a stringed musical instrument, these properties provide for a more durable string that can hold tension and a more consistent tone for a longer period of time. In the case of line for fishing equipment, these properties provide better feel, response, and durability. And in the case of sports racquets, these properties provide better feel, response, increased power, and lower shock resulting from the impact of the object being struck onto the bed of intersecting strings on the racquet.
The current fibers and strings used in this field are made of high strength metallic wires, natural gut fibers made from the intestines of animals, and synthetic fibers made from polymeric materials. The advantages and disadvantages of each are discussed in the following paragraphs. In general strings which are made from high strength metallic fibers offer high break strength, high resiliency, and high abrasion resistance, however they have the disadvantage of having high stiffness, low flexibility, and low ductility. As a result, when used for instance as a string for sports racquets, the low flexibility makes the strings difficult to install, the low ductility causes premature breakage, and the high stiffness (low elasticity) results in high impact forces transmitted to the hand and arm of the player.
Strings made from natural gut fibers offer a high degree of elasticity and resiliency, however they generally lack high breaking strengths and abrasion resistance, and when exposed to moisture in the form of water vapor contained in the air, they lose their strength and the ability to hold tension. Strings made from natural gut strings can be combined with synthetic materials in the form of fibers, bonding resins, and coating resins to improve strength and abrasion resistance, however, when synthetic materials are combined with the natural gut fibers there is in general a corresponding degradation in the elasticity and resiliency of the string. Since strings made from natural gut fibers are also generally more expensive, the performance value of the strings is greatly reduced with the addition of synthetic materials.
Strings made from synthetic fibers are currently the most commonly used due to their relatively low cost and the availability of the material and because the materials can be formulated or engineered to achieve a wide variety of properties. Synthetic strings which are designed for high strength and high abrasion resistance are made from fibers engineered to have higher strengths, and incorporate high strength bonding resins and coating resins. However, these strings also generally have correspondingly high elastic modulus and high dynamic modulus as a result of the viscoelasticity of polymeric materials. Synthetic strings which are designed to have lower stiffness are also generally made from fibers which have high strength and stiffness, however the construction of the string generally incorporates more fibers to build in more elasticity. Unfortunately, strings designed in this matter are generally less resilient, rapidly lose their elasticity over a short period of time, and can not hold tension for long periods of time.
It is also known that additives can be used to lower the stiffness properties of some synthetic polymeric materials at the polymerization stage. These additives also tend to reduce the strength of the bulk material. In addition, due to the extrusion process used to produce most synthetic fibers, additives which can be used to reduce the modulus of elasticity generally cannot be employed since they reduce the molecular weight of the material and adversely affect dimensional stability of the fiber as it is extruded.
Synthetic materials which can be extruded, which have a lower modulus of elasticity and lower dynamic modulus of elasticity, such as those listed in U.S. Pat. No. 4,586,708, generally have lower strengths which limits their application for use as strings for musical instruments, fishing equipment, or sports racquets.
It is also known that strings can be treated during or after manufacture of the string to alter the physical properties of the string. In U.S. Pat. No. 4,015,133, Ferrari discovered that irradiation of strings made from synthetic polyamide materials resulted in strings having higher resiliency, however there was only a minor effect on the modulus of elasticity of the material. It is also known that exposing some polymeric materials such as polyamides to water can soften strings, as a result of the water being absorbed into the material, however, the water also evaporates rapidly and the original physical properties of the material return.
Considering the current state of the art of strings for musical instruments, fishing equipment, and sports racquets there is still a need for an optimum string which provides an optimal combination of elasticity, strength, flexibility, abrasion resistance, ductility, and resiliency.